1. Field of the Invention
This invention relates to compositions comprising novel polysulfide-silane coupling agents, referred to as hydrocarbon core polysulfide silanes, rubber compositions incorporating the novel polysulfide silanes, and methods of preparing the same. The hydrocarbon core polysulfide silanes of the present invention may be used in coupling mineral fillers within elastomeric compositions, particularly rubber, wherein specific characteristics of the polysulfide silanes may be tailored towards specific characteristics of the elastomeric composition.
2. Description of Related Art
Typically, sulfur-containing coupling agents for mineral-filled elastomers involve silanes in which two alkoxysilyl groups are bound, each to one end of a chain of sulfur atoms. The chemical bond in these molecules between the two silicon atoms and sulfur is indirect, being mediated by two similar and, in most cases, identical hydrocarbon fragments. This general silane structure almost invariably relies on a chain of three methylene groups as the two mediating hydrocarbon units, and upon the use of two triethoxysilyl groups. In the most notable exceptions, the methylene chain is shorter, containing only one or two methylenes per chain.
The prior art discloses the composition, preparation, and use of these coupling agents in a number of applications, but primarily as coupling agents for mineral-filled elastomers. These coupling agents function by chemically bonding silica or other mineral fillers to polymer when used in rubber applications. Coupling is accomplished by chemical bond formation between the silane sulfur and the polymer and by hydrolysis of the silane alkoxy groups and subsequent condensation with silica hydroxyl groups.
Canadian Patent Application No. 2,231,302 to Scholl et al. (Scholl et al. ""302) discloses rubber mixtures containing at least one rubber, a filler, optional rubber auxiliaries and at least one polysulphide polyether silane having the formula
R1R2R3Sixe2x80x94X1xe2x80x94(xe2x80x94Sx-polyetherxe2x80x94)mxe2x80x94(xe2x80x94Sxxe2x80x94X2xe2x80x94SiR1R2R3)n
for use in preparing rubber vulcanisates from which are produced low rolling resistance tires having good wet skid resistance and a high abrasion resistance. The rubber mixtures disclosed contain from 0.1 to 10 wt. % of the polysulphide polyether silane. When a mixture of oligomers of the polysulphide polyether silanes are used, the average molecular weight is about 800 to 10,000.
In the case of Scholl et al. ""302, the polyether portions of the molecules, upon standing, may form peroxides which cause degradation of the resultant rubber compositions. Furthermore, the polyether portions of the silane compete with other rubber constituents.
Thus, it would be advantageous to provide a novel polysulfide composition having more than two silyl groups without the necessity of ether linkages for enhanced performance in filled elastomer compositions, rubber compositions, and use in tire compositions.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a novel polysulfide silane composition having more than two silyl groups and a method of making the same.
It is another object of the present invention to provide a non-collinear polysulfide silane composition to provide enhanced dispersibility of the filler within an elastomeric composition, rubber compositions, and tire compositions and a method of making the same.
A further object of the invention is to provide a filled elastomeric composition, rubber composition and tire compositions containing a polysulfide silane having improved filler dispersion.
It is yet another object of the present invention to provide a low rolling resistance tire having enhanced performance.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a polysulfide silane composition having the formula:
(X1X2X3Sixe2x80x94Jxe2x80x94Sxxe2x80x94)pxe2x80x94G
wherein p is 3 to 12, x is 2 to 20, X1 is a hydrolyzable functionality selected from the group consisting of xe2x80x94Cl, xe2x80x94Br, xe2x80x94OH, xe2x80x94Oxe2x80x94Nxe2x95x90C(R)2, xe2x80x94OR, and RC(xe2x95x90O)Oxe2x80x94, in which R is a hydrocarbon fragment obtained by removing one hydrogen atom from a hydrocarbon having 1 to 20 carbon atoms, X2 and X3 are X1, R or H, J is a hydrocarbon fragment obtained by removal of one hydrogen atom of R, and G is a hydrocarbon fragment obtained by removal of a p quantity of hydrogen atoms of a hydrocarbon having from 1 to 30 carbon atoms.
Preferably, X1, X2 and X3 are the same hydrolyzable functionalities with ethoxy being most preferred. Alternatively, X1, X2 and X3 may also each be different hydrolyzable functionalities. Preferably, p is 3 to 6; x is 2 to 8; R is a hydrocarbon functionality selected from the group consisting of straight chain alkyl, alkenyl, aryl and aralkyl groups; and J is selected from the group consisting of methylene, ethylene, propylene, isobutylene, and diradicals obtained by loss of hydrogen atoms at a 2,4 or 2,5 position of norbornane, an alpha position of 2-norbornylethane, a beta position of 2-norbornylethane, a 4 position of 2-norbornylethane, or a 5 position of 2-norbornylethane.
When p is 3 and G is preferably glyceryl. Alternatively, G may be a hydrocarbon fragment obtained by removal of 3 hydrogen atoms from 2-norbornylethane. G may also be a hydrocarbon fragment obtained by removal of 3 hydroxyl groups from a trimethylolalkane. When p is 4 and G is preferably pentaerythrityl. Alternatively, G may be a hydrocarbon fragment obtained by removal of 4 hydrogen atoms from 2-norbornylethane. When p is greater than 4 and G may be a hydrocarbon fragment obtained by removal of more then 4 hydrogen atoms from a hydrocarbon selected from the group consisting of cyclododecane, triethylcyclohexane, 2,6-dimethyloctane, and squalane. G may also contain a tertiary amine functionality or a cyano functionality.
In a second aspect, the present invention is directed to a polysulfide silane composition comprising one or more isomers of tetrakis-1,3,4,5-(3-triethoxysilyl-1-propyltetrathio)neopentane.
In a third aspect, the present invention is directed to a polysulfide silane composition comprising one or more isomers of tris-1,2,3-(3-triethoxysilyl-1-propyltetrathio)propane.
In a fourth aspect, the present invention is directed to a process of making a hydrocarbon core polysulfide silane having the formula
(X1X2X3Sixe2x80x94Jxe2x80x94Sxxe2x80x94)pxe2x80x94G
wherein p is 3 to 12, x is 2 to 20, X1 is a hydrolyzable functionality selected from the group consisting of xe2x80x94Cl, xe2x80x94Br, xe2x80x94OH, xe2x80x94Oxe2x80x94Nxe2x95x90C(R)2, xe2x80x94OR, or RC(xe2x95x90O)Oxe2x80x94, in which R is a hydrocarbon fragment obtained by removing one hydrogen atom from a hydrocarbon having 1 to 20 carbon atoms, X2 and X3 are X1, R or H, J is a hydrocarbon fragment obtained by removal of one hydrogen atom of R, and G is a hydrocarbon fragment obtained by removal of a p quantity of hydrogen atoms of a hydrocarbon having from 1 to 30 carbon atoms, comprising the steps of: providing a mercaptan; deprotonating the mercaptan; providing a source of elemental sulfur; forming a reactive sulfur anion by reacting the deprotonated mercaptan with the elemental sulfur; and coupling the reactive sulfur anion with a carbon containing substrate.
Preferably, the step of providing the mercaptan comprises providing a mercaptan having a formula X1X2X3Sixe2x80x94Jxe2x80x94SH wherein the mercaptan is most preferably selected from the group consisting of 3-mercapto-1-propyltriethoxysilane and 3-mercapto-1-propylmethyldiethoxysilane.
Alternatively, the step of providing the mercaptan comprises providing a mercaptan having a formula (HSxxe2x80x94)pG wherein the mearcaptan is most preferably selected from the group consisting of 2,2-bis(mercaptomethyl)-1,3-dimercaptopropane and 1,2,3-trimercaptopropane.
The step of deprotonating the mercaptan may comprise deprotonating the mercaptan with a Brxc3x6nsted base using p equivalents of the base for each mole of mercaptan or with an amine type base.
Most preferably, the step of forming the reactive sulfur anion is sufficiently complete prior to introduction of the carbon containing substrate.
In a fifth aspect, the present invention is directed to an elastomeric composition comprising at least one hydrocarbon core polysulfide silane having the formula:
(X1X2X3Sixe2x80x94Jxe2x80x94Sxxe2x80x94)pxe2x80x94G
wherein p is 3 to 12, x is 2 to 20, X1 is a hydrolyzable functionality selected from the group consisting of xe2x80x94Cl, xe2x80x94Br, xe2x80x94OH, xe2x80x94Oxe2x80x94Nxe2x95x90C(R)2, xe2x80x94OR, or RC(xe2x95x90O)Oxe2x80x94, in which R is a hydrocarbon fragment obtained by removing one hydrogen atom from a hydrocarbon having 1 to 20 carbon atoms, X2 and X3 are X1, R or hydrogen, J is a hydrocarbon fragment obtained by removal of one hydrogen atom of R, and G is a hydrocarbon fragment obtained by removal of a p quantity of hydrogen atoms of a hydrocarbon having from 1 to 30 carbon atoms; an unsaturated organic polymer; and a filler.
Preferably, the at least one hydrocarbon core polysulfide silane is one or more isomers of tetrakis-1,3,4,5-(3-triethoxysilyl-1-propyltetrathio)neopentane or tris-1,2,3-(3-triethoxysilyl-1-propyltetrathio)propane. Most preferably, the at least one hydrocarbon core polysulfide silane is present in an amount of about 0.05 to about 25 phr.
The elastomeric composition preferably comprises a filler present in an amount of about 1 to about 85 wt. % carbon black based on a total weight of the filler and at least one hydrocarbon core polysulfide silane is present in an amount of about 0.1 to about 20 wt. % of the hydrocarbon core polysulfide silane based on a total weight of the filler.
In a sixth aspect, the present invention is directed to a method of making a rubber composition comprising the steps of providing at least one isomer of a hydrocarbon core polysulfide silane having the formula
(X1X2X3Sixe2x80x94Jxe2x80x94Sxxe2x80x94)pxe2x80x94G
wherein p is 3 to 12, x is 2 to 20, p is 3 to 12, x is 2 to 20, X1 is a hydrolyzable functionality selected from the group consisting of xe2x80x94Cl, xe2x80x94Br, xe2x80x94OH, xe2x80x94Oxe2x80x94Nxe2x95x90C(R)2, xe2x80x94OR, and RC(xe2x95x90O)Oxe2x80x94, in which R is a hydrocarbon fragment obtained by removing one hydrogen atom from a hydrocarbon having 1 to 20 carbon atoms, X2 and X3 are X1, R or H, J is a hydrocarbon fragment obtained by removal of one hydrogen atom of R, and G is a hydrocarbon fragment obtained by removal of a p quantity of hydrogen atoms of a hydrocarbon having from 1 to 30 carbon atoms; providing an organic polymer; providing a filler; thermomechanically mixing the organic polymer, filler and hydrocarbon core polysulfide silane to form a rubber mixture; curing the rubber mixture to form a rubber composition having enhanced dispersion of the filler.
Preferably, during the step of providing the filler, the filler has been pretreated with all or a portion of the at least one isomer of the hydrocarbon core polysulfide silane.
The process may further include the step of adding curing agents to the rubber mixture in another thermomechanical mixing stage.
Preferably, the hydrocarbon core polysulfide silane is one or more isomers of tetrakis-1,3,4,5-(3-triethoxysilyl-1-propyltetrathio)neopentane or one or more isomers of tris-1,2,3-(3-triethoxysilyl-1-propyltetrathio)propane.
In a seventh aspect, the present invention is directed to a filler for dispersion in elastomeric compositions comprising: mineral particulates; and at least one hydrocarbon core polysulfide silane having the formula:
(X1X2X3Sixe2x80x94Jxe2x80x94Sxxe2x80x94)pxe2x80x94G
wherein p is 3 to 12, x is 2 to 20, X1 is a hydrolyzable functionality selected from the group consisting of xe2x80x94Cl, xe2x80x94Br, xe2x80x94OH, xe2x80x94Oxe2x80x94Nxe2x95x90C(R)2, xe2x80x94OR, or RC(xe2x95x90O)Oxe2x80x94, in which R is a hydrocarbon fragment obtained by removing one hydrogen atom from a hydrocarbon having 1 to 20 carbon atoms, X2 and X3 are X1, R or H, J is a hydrocarbon fragment obtained by removal of one hydrogen atom of R, and G is a hydrocarbon fragment obtained by removal of a p quantity of hydrogen atoms of a hydrocarbon having from 1 to 30 carbon atoms.
Preferably, the mineral particulates are siliceous particulates. The filler of this aspect may further comprise carbon black. Preferably, the at least one hydrocarbon core polysulfide silane is one or more isomers of tetrakis-1,3,4,5-(3-triethoxysilyl-1-propyltetrathio)neopentane or one or more isomers of tris-1,2,3-(3-triethoxysilyl-1-propyltetrathio)propane.